Supplemental table S1. Herd visits and results M. bovis

<i>Mycoplasma (M.) bovis</i> causes severe diseases amongst cattle. Sweden has a favorable situation for control of this disease with a low prevalence of <i>M. bovis</i> infected and seropositive herds detected only in the southern parts of the country. To prevent the spread of the infection, analyzing antibody levels is a cost-effective method to determine herd pathogen exposure status. In this study our aims were to monitor the antibody dynamics in infected herds over time using IDvet ELISA, to both evaluate risk-based sampling and investigate the impact of <i>M. bovis</i> exposure on health and production. We visited and sampled 35 dairy herds, 31 of which were sampled at least twice and 26 sampled four times and followed for two years. The patterns of herd seroprevalence varied depending on the status prior to the herd’s entry into the study and remained relatively stable at the herd level, although antibody status could differ among age groups. Overall, herds with high exposure prevalence (90-100%), indicated by a positive BTM test, and herds with low exposure prevalence (5-10%), characterized by a few positive cows, maintained their exposure status throughout the study. The changes in status observed within the herds, both among calves and cows, included transitions from positive to negative as well as from negative to positive. In five herds, the calf group transitioned from positive to negative, while in one herd, the reverse occurred. Three herds exhibited an increase in antibody levels; in two of these herds, the cows transitioned from negative to positive, and in one herd with positive cows the calves shifted from negative to positive. A cost-effective test strategy to find likely infected herds involved sampling BTM and cows with a high SCC which gave a 90% probability of locating infected herds by the second sampling. Milk production was reduced by 404 kg (1.3 L/day, <i>p</i>=0.012) in cows positive for <i>M. bovis</i> antibodies. Therefore, controlling the spread of <i>M. bovis</i> infection will likely have a positive impact on reducing income loss for dairy herds in Sweden.